move / reorder UIList items don't work
Use CollectionProperty.move()

The code to move the collection property items is missing. scene.custom.move(0, 1) will swap items with indices 0 and 1.

        if self.action == 'DOWN' and idx &lt; len(scn.custom) - 1:
            item_next = scn.custom[idx+1].name
            scn.custom.move(idx, idx + 1)
            scn.custom_index += 1
            info = 'Item %d selected' % (scn.custom_index + 1)
            self.report({'INFO'}, info)

        elif self.action == 'UP' and idx &gt;= 1:
            item_prev = scn.custom[idx-1].name
            scn.custom.move(idx, idx-1)
            scn.custom_index -= 1
            info = 'Item %d selected' % (scn.custom_index + 1)
            self.report({'INFO'}, info)